Transmission Control Protocol (TCP) is a commonly used communication protocol used for communicating packet data from one data processing system to another over a data network. Internet Protocol (IP) is an addressing protocol to handle the addressing of the TCP data packets. Together, the layers of the two protocols are implemented as a TCP/IP stack for constructing, sending, and receiving the packets from one data processing system to another data processing system across data networks.
IP version 4 (IPv4) is the fourth version of IP which sets out internet addresses in the form of four octets. An octet is eight bits (each bit capable of representing a binary 0 value or a binary 1 value). The 32-bit IPv4 address takes the form of “A.B.C.D”, where A, B, C, and D are each an octet. Each octet is capable of representing 256 Base 10 values, 0-255. The Base 10 value 0 is a reserved value of an octet and usually indicates a group of other Base 10 numbers of a subnet that are permissible in that octet. A subnet is a part of a network in which at least one octet of the addressing is common with other parts of the network, and a differing octet takes on different values within the part.
Hereinafter, a reference to a first octet is a reference to the “A” octet in the above IPv4 representation. Similarly, a reference to a second octet is a reference to the “B” octet, a reference to a third octet is a reference to the “C” octet, and a reference to a fourth octet is a reference to the “D” octet in the above IPv4 representation. For example, in an example IP address 192.168.1.2, the first octet has the value 192 in Base 10, the second octet has the value 168 in Base 10, the third octet has the value 1 in Base 10, and the forth octet has the value 2 in Base 10. Hereinafter, unless an octet is represented in binary, or unless expressly distinguished where used, a value of an octet refers to a Base 10 value represented in the octet.
Some IPv4 address spaces are reserved for internal use within a local area network (LAN). For example, 192.0.0.0 and 10.0.0.0 are two address spaces which are supposed to be configured for uniqueness within only a LAN, and are not supposed to be unique across Wide Area Networks (WAN). Internet Engineering Task Force (IETF) document ‘Request for Comments-1918’ (RFC-1918) identifies that the following IPV4 address ranges have been reserved by Internet Assigned Numbers Authority (IRNA) for private Internets: 10.0.0.0/8, 172.16.0.0/12, and 192.168.0.0/16. Therefore, as an example, two different LANs can each implement 10.x.y.z address, e.g., 10.2.3.4, such that 10.2.3.4 will be uniquely associated with a network interface of a target system or application, the uniqueness being valid only with each respective LAN.